This application claims the priority of Korean Patent Application No. 2002-28024, filed May 21, 2002 in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety.
1. Field of the invention
The present invention generally relates to an image projecting apparatus using a dichroic mirror wheel, and more particularly, it relates to an image projecting apparatus capable of minimizing a light loss and improving brightness by using a pair of dichroic mirror wheels, and a method therefor.
2. Description of the Prior Art
Apparatuses like a projector or a projection system are types of displays that realize a predetermined image on a screen by projecting a light generated at a light source onto the screen through an optical system. Such displays are used in many places, namely, in meetings for presentations, in theaters and in homes.
An optical device such as a projector realizes an image by using a liquid crystal display (LCD) or a cathode ray tube (CRT). In order to accomplish a large-sized screen, conventionally, the optical device magnifies the image on the LCD and CRT, and projects the magnified image on the screen. This method merely magnifies the image, but cannot provide a clear image. In order to solve this problem, an image projecting device using a digital micromirror device (DMD) has been suggested and is presently in use.
The DMD has a number of micrormirrors corresponding to the resolution. The micromirrors control the reflection of light in accordance with the input signals. Briefly put, the DMD is a semiconductor optical switch using a micromirror. As the DMD is digital, it has excellent color representation and brightness.
FIG. 1 is a view showing a basic structure of a conventional projection type image apparatus using a color wheel.
Referring to FIG. 1, the conventional projection type image apparatus 100 using the color wheel includes a light source 110, a color wheel 120, a light tube 130, a lens 140, a DMD panel 150 and a projection lens 160. The one-dotted line in FIG. 1 represents an optic path of white light.
The light source 110 can be an arc lamp or a laser, which emits a white light. The color wheel 120 is rotated in the arrowed direction by a rotating means (not shown), and divided into a red (R), green (G) and blue (B) divisions. The white light emitted from the light source 110 is passed through the R, G and B divisions into split rays of light, i.e., R, G and B beams.
The light tube 130 is formed as a hollow hexahedron having a through hole therein. The R, G and B beams from the color wheel 120 are transformed into a square beam inside of the light tube 130. The square beam of the light is dispersed at the lens 140 to be incident on the DMD panel 150.
The DMD panel 150 includes a plurality of micromirrors 150a. The R, G and B beams of respective wavelength are reflected from the micromirrors 150a of the DMD panel 150. The reflected R, G and B beams pass through the projection lens 160 and form an image on the screen.
Such a projection type image apparatus 100 can quickly process the response signal to the split R, G and B beams by the independently-driven micromirrors 150a. In other words, color image of good quality can be obtained with a simpler structure. However, realizing an image using a color filter and single-plate type DMD panel usually utilizes only a third of the entire light quantity.
This is because 60-70% of the white light emitted from the light source is blocked at the color wheel 120. While the R beam is evenly projected on the entire panel, other beams, i.e., G and B are completely blocked by the color filter and discarded. The same situation applies with respect to the G and B beams, respectively.
Accordingly, only a third of the incident white light is utilized according to the color filter method, and the brightness of the image is deteriorated to a third. In other words, as the white light is emitted from the light source, passed through the color wheel and then projected onto the panel, the entire light quantity decreases. Accordingly, the light utilization decreases, and brightness of the realized image is also deteriorated.
Accordingly, it is an aspect of the present invention to provide an image projecting apparatus and method capable of preventing a reduction of light utilization on the single panel to a third degree, and increasing a light quantity utilization using a pair of dichroic mirror wheels.
In order to accomplish the above aspect, an image projecting apparatus consistent with the present invention includes a light source which emits a plurality of monochromatic rays of light with different wavelengths, a condenser lens which concentrates the plurality of monochromatic rays, a first color separating unit which rotates and selectively causes the plurality of monochromatic rays to be reflected therefrom or passed therethrough, a second color separating unit which selectively causes the plurality of monochromatic rays passed through the first color separating unit to be reflected therefrom or passed therethrough, a plurality of square beam generating units which are inputted with the plurality of monochromatic rays reflected from the first and the second color separating units and which transform the monochromatic rays as inputted into square beams, a plurality of panel units which are inputted with the square beams of the monochromatic rays and which form a plurality of monochromatic images corresponding to the monochromatic rays, and a plurality of projecting lens units which are disposed to face the plurality of panel units.
The first and the second color separating units each comprises a dichroic mirror wheel. Each of the plurality of panel units is inputted with the plurality of monochromatic rays, which are reflected from the first and the second color separating units by predetermined order, at least once, thereby forming an image thereon.
Each of the first and the second color separating units is divided into a plurality of divisions where the plurality of monochromatic rays are selectively reflected from or passed through. The number of the plurality of divisions is a multiple of three (3).
The first and the second color separating units are rotated at a same speed so that the plurality of monochromatic rays of different wavelengths can be reflected and passed on the same optical axis. Each of the first and the second color separating units corresponds to a basal part of a solid cone by cutting off a top by a plane parallel to the base. The plurality of panel units each comprises a digital micromirror device (DMD) for modulating the plurality of monochromatic images into a digital signal, and reflecting the signal to the plurality of projecting lens units at a predetermined angle.
According to the present invention, by employing two dichroic mirror wheels, the R, G and B monochromatic lights are selectively reflected from, or passed through the two dichroic mirror wheels according to wavelengths. As a result, independent images, or identical images can be realized on a plurality of screens even in a single panel optical device system.
An image projecting method according to another embodiment of the present invention includes emitting a plurality of monochromatic rays of light with different wavelengths through a light source, concentrating the plurality of monochromatic rays through a condenser lens, rotating and selectively causing the plurality of monochromatic rays to be reflected from or passed through a first color separating unit, selectively causing the plurality of monochromatic rays passed through the first color separating unit to be reflected from or passed through a second color separating unit, inputting a plurality of square beam generating units with the plurality of monochromatic rays reflected from the first and the second color separating units and transforming the monochromatic rays as inputted into square beams, inputting a plurality of panel units with the square beams of the monochromatic rays and forming a plurality of monochromatic images corresponding to the monochromatic rays, and disposing a plurality of projecting lens units to face the plurality of panel units.
An image projecting apparatus according to another embodiment of the present invention includes means for emitting a plurality of monochromatic rays of light with different wavelengths, means for concentrating the plurality of monochromatic rays, means for rotating and selectively causing the plurality of monochromatic rays to be reflected therefrom or passed therethrough, means for selectively causing the plurality of monochromatic rays passed through the first color separating unit to be reflected therefrom or passed therethrough, means for being inputted with the plurality of monochromatic rays reflected from the first and the second color separating units and transforming the monochromatic rays as inputted into square beams, means for being inputted with the square beams of the monochromatic rays and forming a plurality of monochromatic images corresponding to the monochromatic rays, and means for projecting being disposed to face the plurality of panel units.
An image projecting apparatus according to another embodiment of the present invention includes a light source which emits a plurality of monochromatic rays of light with different wavelengths, a condenser lens which concentrates the plurality of monochromatic rays, a first dichroic mirror wheel which rotates and selectively causes the plurality of monochromatic rays to be reflected therefrom or passed therethrough, a second dichroic mirror wheel which selectively causes the plurality of monochromatic rays passed through the first color separating unit to be reflected therefrom or passed therethrough, a plurality of square beam generating units which are inputted with the plurality of monochromatic rays reflected from the first and the second dichroic mirror wheels and which transform the monochromatic rays as inputted into square beams, a plurality of digital micromirror devices DMD""s which are inputted with the square beams of the monochromatic rays and form a plurality of monochromatic images corresponding to the monochromatic rays and a plurality of projecting lens units disposed to face the plurality of DMD""s.